Petroleum fuel oil and black liquor combustion

ABSTRACT

THE EFFICIENCY OF PROCESSES INVOLVING THE BURNING OF PETROLEUM FUEL OILS AND HIGH SOLIDS CONTENT BLACK LIQUOR IS IMPROVED BY ADDING N,N-DIMETHYLAMIDES OF UNSATURATED CARBOXYLIC ACIDS TO THE PETROLEUM FUEL OILS AND BLACK LIQUOR.

'UnitedStates Patent Int. Cl. C101 1/18 US. Cl. 44--66 14 Claims ABSTRACT OF THE DISCLOSURE The efficiency of processes involving the burning of petroleum fuel oils and high solids content black liquor is improved by adding N,Ndimethylamides of unsaturated carboxylic acids to the petroleum fuel oils and black liquor.

This invention relates to the burning of petroleum fuel oils and high solids content black liquor and, more particularly, it constitutes an improvement over known processes involving the burning of the heavier grades of petroleum fuel oils such as those designated No. and No. 6 fuel oils and high solids content black liquor.

Stated briefly, black liquor, as is well known to those skilled in the art of papermaking by alkaline pulping processes, is the spent cooking liquor from the digesters plus the filtrate from the Washing operation. It is concentrated first in a multiple effect evaporator, next in a cascade or cyclone evaporator (a direct heat transfer device), then further concentrated by adding thereto a salt cake makeup and collected dust from the flue gas and hoppers, and finally heated prior to firing in the furnace. Inorganic components (sodium salts) in the concentrated black liquor are recovered in this burning operation as molten ash or smelt for reuse in the cooking liquor. Since all of these operations are well known in the art, a discussion thereof will not be repeated here. For a detailed description of these processes, reference is made to Tappi Monograph Series No. 32 edited by Roy P. Whitney, Chemical Recovery in Alkaline Pulping Processes, Mack Printing Co., Easton, Pa., 1968, particularly chapters 2 and 3 thereof, which reference is hereby made a part of this application.

As heretofore practiced, however, operations involving the concentration (particularly if the concentrate so produced has a high solids content), chemical recovery, and burning of black liquor have presented certain practical diificulties. For example, when attempts have been made to operate a cascade or cyclone evaporator so as to produce a black liquor having a solids content greater than 60 percent, the results have generally been an increase in power required for rotating the tubular elements of the evaporator and ultimately severe plugging of the furnace nozzles. From the evaporator, the heavy black liquor is fed into the furnace or combustion chamber which is perhaps the most important single piece of equipment in the entire recovery unit. As its ultimate goal this unit should be capable of performing the following functions:

(1) Dehydrating the heavy black liquor and burning the organic components thereof with maximum combustion efficiency,

(2) Reducing that portion of the chemicals present as sodium sulfate and other sodium-sulfur-oxygen compounds to sodium sulfide,

(3) Melting the inorganic chemicals for continuous removal in molten form, and

(4) Conditioning the products of combustion to reduce chemical carryover causing air pollution.

In order to attain maximum combustion efficiency as practiced by the prior art, it has been necessary to introduce a high solids content black liquor into the furnace.

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Although this procedure tends to increase combustion efiiciency, the results have not been entirely satisfactory. For example, a high solids content black liquor is very viscous. When such a liquor strikes the impingement area of the oscillator, it falls directly to the smelt zone, thus reducing combustion efficiency. Furthermore, under these conditions the amount of particulate matter as dust and fume going to the stack is high. Unless some means are taken to recover this particulate matter, it will pass through the stack into the atmosphere, thus not only contributing to air pollution but representing an economic loss.

Two accepted methods have been proposed for the recovery of this particulate matter. One employs an electrostatic precipitator and the other makes use of a venturi evaporator-scrubber. While these devices are more or less efficient, their use increases capital operating costs and imposes an additional duty upon the mill operator.

It is, therefore, a principal object of the present invention to provide a method for the burning of concentrated black liquor that obviates the disadvantages of the prior art processes.

It is yet another object of this invention to provide a relatively inexpensive and simplified process whereby the amount of particulate matter going to the stack is reduced.

These and other objects and advantages will become apparent as the description proceeds.

To the accomplishment of the foregoing and related ends, this invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various Ways in which the principles of the invention may be employed.

Briefly stated, I have discovered that the addition of a relatively small amount of N,N-dimethylamides of straight chain unsaturated carboxylic acids to black liquor prior to its addition to the cascade or cyclone evaporator permits the operation of the evaporator so as to produce a black liquor having a solids content in excess of 60 percent free of the attendant disadvantages usually encountered when it is so operated, thus increasing the combustion efficiency of the furnace and alleviating air pollution.

It would be expected that the addition of the dimethylamides as defined above to the cooking chemicals used in the preparation of chemical pulp from wood chips in the amounts taught by S. J. Buckman et al. in US. Pat. 3,448,004 would be carried through the entire pulping operation including the chemical recovery process, thus improving the efficiency of processes involving the burning of concentrated black liquor. I have found, however, that this expected result does not follow. While I do not wish to be bound by any theory as to why the foregoing is true, I believe the correct explanation of this result is substantially as follows: In all probability, some of the dimethylamides added as a pulping aid to the cooking chemicals used in the preparation of chemical pulp from cellulosic materials will be destroyed prior to the conclusion of the cooking process. Finally, any dimethylamides not so destroyed will be largely removed along with the soap in the soap skimming tank.

Suitable N,N-dirnethylamides of straight chain carboxylic acids are those prepared from carboxylic acids containing 18 carbon atoms. The acids are further characterized by having at least one carbon to carbon double bond. Specific acids classified within this category include: oleic, linoleic, linolenic, ricinoleic, and mixtures thereof. The N,N-dimethylamides of the foregoing acids are identified as N,N-dirnethyloleamide, N,N-dimethyllinoleamide, N,N-dimethyllinolenamide, and N,N-dimethylncinoleamide, respectively. Also suitable are the mixed acids found in tall, castor, corn, cottonseed, linseed, olive, peanut, rapeseed, safllower, sesame, and soybean oils. A mixture of carboxylic acids particularly suitable for use in my invention is that available commercially as tall oil fatty acids under the trademark Uinitol ACD. A typical analysis of this product is as follows:

TABLE I Specification Typical range analysis Fatty acids percent 08. 8-09. 7 98. 9 Rosin acids percent 0. 2-0. G 0. 5 Unsaponifiables percent... 0. 1-0. 6 0. G Linoleic acid percent 45 Oleic acid percent 51 Saturated acid percent 2. -2.8 2.4 Acid number 108-20l 100 Saponification number 198-202 200 Color Gardner 34 3+ 'Viscosity:

ss,U 100 F 105 Gardner seconds 0. 0 Specific gravity, 60 F./60 F 0. 005 Titre, 0..-... 0.0 Flask point F 375 Fire point, F 435 The dimethylamides of these tall oil fatty acids will hereinafter be referred to merely as dimethylamide.

When the dimethylamides are used to increase combustion etficiency and decrease the amount of particulate matter going to the stack, these amides may be added to the cyclone, to the venturi scrubber, or preferably to the salt cake mixer.

In another aspect of my invention, I have discovered that the burning eificiency of petroleum fuel oils, particularly the heavier grades thereof, such as No. and the yet heavier No. 7 or Bunker C may be increased by the addition of a relatively small amount of a dimethylamide as previously described to the fuel oil.

As to the amount of the dimethylamide to be added to the black liquor or fuel oil, suitable quantities vary from about 10 to about 500 parts per million parts of black liquor or fuel oil. Preferably the amount used varies from about to 100 parts per million parts of black liquor or fuel oil.

In order to disclose the nature of the invention still more clearly, the following illustrative examples will be given. It is understood, however, that the invention is not to be limited to the specific conditions or details set forth in these examples, except insofar as such limitations are specified in the appended claims.

EXAMPLE 1 In this example the effectiveness of dimethylamide as an aid in processes involving the burning of high solids black liquor was determined by comparing the results of a series of runs in the presence of dimethylamide to a similar series of runs in the absence of that compound.

In the absence of dimethylamide the particular mill at which these tests were conducted was able to process a maximum of about 240,000 gallons of black liquor per day. At the end of 14 days, it was necessary to shut down the plant and remove the deposits formed on the heat exchange tubes of the recovery boiler.

After the equipment was cleaned, the tests were repeated with the exception that parts of dimethylamide per million parts of black liquor was added to the black liquor at the salt cake mixer. In this series of runs using dimethylamide in the process, it was not only possible to increase the average throughput of black liquor to 250,000 gallons per day (a 4% increase) but, in addition, deposit formation on the heat exchange tubes of the recovery boiler was inhibited. The latter is evident from the fact that even at the increased throughput the equipment could be operated for a period of 27 days before it became necessary to shut down the plant for deposit removal.

At a second mill a maximum of about 226,000 gallons of black liquor was processed per day when operated in the absence of dimethylamide. In addition, under these conditions the screen extending from the base of the salt cake mixer to the top thereof became plugged within a relatively short period of time necessitating its periodic cleaning. When dimethylamide was used at a rate of 25 parts per million parts of the black liquor, the throughput was increased to about 243,000 gallons per day and, furthermore, there was no plugging of the above mentioned screen.

At a third mill a maximum of about 5,200 gallons of high solids content black liquor was processed per hour when operated in the absence of dimethylamide. When dimethylamide was added to the system at the salt cake mixer in an amount equal to 25 parts per million parts of black liquor, it was possible to increase black liquor throughput to about 5,580 gallons per hour. This represented an increase of about 7.1 percent.

At a fourth mill after physically cleaning the recovery furnace boiler, it was possible to process a maximum of 4,840 gallons of high solids content black liquor per hour over a period of 103 hours. When dimethylamide was added to the black liquor at the salt cake mixer in an amount equal to 25 parts per million parts of black liquor and operated continuously over a period of 94 hours, it was possible to operate at a rate equal to 5,270 gallons of black liquor per hour. This represented an increase in throughput of about 8.8 percent.

At the four mills the black liquor flowing from the salt cake mixer in the absence of dimethylamide was very viscous, an objectionable feature because the final result is incomplete combustion in the furnace. I found much to my surprise that the addition of dimethylamide to this liquor in an amount varying from about 10 to 500 parts, preferably 15 to parts, per million parts of black liquor reduced its viscosity, thus alleviating to a large extent many of the difliculties encountered in the burning of black liquor.

To confirm the observation in the laboratory, the viscosity of black liquor samples containing 68 percent solids and varying amounts of dimethylamide was determined by means of a 'Brookfield viscometer at 100 C. operated at a speed of 60 revolutions per minute. The experiments together with the results are summarized in Table 2.

Concentration of DMA,

Relative viscosity, Decrease in parts per million ccntipoises viscosity, percent EXAMPLE 2 The experimental procedures summarized in Example 1 were repeated in which the N,N-dimethylamides of the mixed acids found in castor, corn, cottonseed, linseed, olive, peanut, and soybean oils were used instead of the N,N-dimethylamides of tall oil fatty acids. The results were similar to those obtained in Example 1.

It is also my belief that one of the reasons the burning efiiciency of petroleum fuel oils of the heavier grades is improved is because the addition of dimethylamide thereto reduces the viscosity of such fuels. Ordinarily, these fuel oils being very viscous must be preheated before burning. I have found that when dimethylamide is added to these fuels in the amounts stated the degree of preheating necessary for efficient burning may be reduced greatly and in some cases, preheating may be eliminated entire y.

TABLE 3.VISCOSITY OF NO. 6 FUEL OIL CONTAINING VARYING AMOUNTS OF DIMETHYLAMIDE Decrease in viscosity, percent Concentration of DMA, parts per million Relative viscosity, centipolses Similar changes in the viscosity of No. 6 fuel oil were observed when the dimethylamides of the fatty acids previously listed were substituted for dimethylamides of tall oil fatty acids.

While particular embodiments of the invention have been described, it 'will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover by the appended claims any such modifications as fall within the true spirit and scope of the invention.

The invention having thus been described, what is claimed and desired to be secured by Letters Patent is:

1. A process of burning a viscous liquid fuel selected from the group consisting of petroleum fuel oil and black liquor comprising:

adding to said fuel an N,N-dimethylamide of an 18 carbon straight chain unsaturated carboxylic acid in an amount sufiicient to increase the combustion efiiciency of the process; and

burning said fuel containing the added N,N-dimethylamide.

2. The process of claim 1 wherein the fuel is a high solids content black liquor and the dimethylamide is added in an amount of from about 15 to about 100 parts per million parts of black liquor.

3. The process of claim 1 wherein the fuel is petroleum fuel oil and the dimethylamide is added in an amount of from about 15 to about parts per million parts of petroleum fuel oil.

4. The process of claim 1 wherein the straight chain carboxylic acid is a mixture of straight chain carboxylic acids containing 18 carbon atoms and at least one carbon to carbon double bond.

5. The process of claim 1 wherein the straight chain carboxylic acid is a mixture of acids derived from t'all oil.

6. The process of claim 1 wherein the straight chain carboxylic acid is a mixture of acids derived from linseed oil.

7. The process of claim 1 wherein the straight chain carborylic acid is a mixture of acids derived from soybean oil.

8. The process of claim 1 wherein the straight chain carboxylic acid is a mixture of acids derived from cottonseed oil.

9. The process of claim 1 wherein the straight chain carboxylic acid is a mixture of acids derived from corn oil.

10. The process of claim 1 wherein the straight chain carboxylic acid is a mixture of acids derived from peanut oil.

11. The process of claim 1 wherein the N,N-dimethylamide is N,N-dimethyloleamide.

12. The process of claim 1 wherein the N,N-dimethylamide is N,N-dimethyllinoleamide.

13. The process of claim 1 wherein the N,N-dimethy1 amide is N,N-dimethyllinolenamide.

14. The process of claim 1 wherein the N,N-dimethy1- amide is N,N-dimethylricinoleamide.

References Cited UNITED STATES PATENTS 2,744,812 5/1956 Coulter, Jr. et a1. 23-277 R 3,448,004 6/1969 Buckman et al. 162-76 3,304,162 2/ 1967 Marvel, Jr. 44--66 3,150,941 9/1964 Kautsky et a1 44-66 1,692,784 11/1928 Orelup et all. 44-66 DANIEL E. WYMAN, Primary Examiner Y. H. SMITH, Assistant Examiner US. Cl. X.R. 44-50 

